Description

A set of points on the lunar surface whose three dimensional selenodetic coordinates (latitude, longitude, and radial position) have been determined by careful measurement. Typically the points consist of very small craters. Historically, lunar control networks were first established by careful observation, at the eyepiece, of the positions of such features on images obtained with varying librations (apparent tilts of the lunar axes relative to the Earth). Later, measurements were made on photographs, first using ones taken from Earth, and later from known positions in space. Unified Lunar Control Networks typically try to "unify" (reconcile and or adjust) several such networks to match one another as well as possible.

Chronology of Lunar Control Networks

The following is based, in large part, on the material in Sections 1.1 and 3 of Schimerman (1973), supplemented by other sources.

Mayer (1748)

Tobias Mayer seems to have been the first to systematically measure the x-y positions of lunar features using a micrometrically-controlled device in the image space of his telescope; although Montanari, before him, seems to have used some sort of grid to estimate the positions at which to place features on his map. Mayer first tracked the Moon’s librations by following the position of Manilius, and then carefully measured 23 other points and estimated the positions of 65 more relative to those.

Bouvard and Arago (1806)

Bouvard and Arago made 18 more measures of Manilius, with Bouvard continuing the work and reporting improved values for the librations in 1816 and 1818.

Nicollet (18??)

Nicollet combined his 32 measures of Manilius with the 142 others available, to obtain still better values for the librations.

Lohrmann (1822-1826)

To prepare an accurate lunar map, Lohrmann used an eyepiece micrometer to measure the positions of 79 points relative to the limb.

Beer and Mädler (18??)

Mädler used Beer’s four-inch refractor to measure the position, with an eyepiece micrometer, of 106 lunar features, and estimated the heights and positions of many more. He directly measured the diameters of 150 craters. He introduced the practice, on his maps, of using uppercase letters to indicate features whose positions had been carefully measured, and lowercase letters to indicate ones whose positions were guessed at.

Bessel and Schlüter (1839-1846)

Bessel began the practice of studying the Moon’s librations by repeated measurements of Mösting A (as a replacement for the less clearly defined Manilius). His two initial series of measurements using the 6.25-inch heliometer (a refractor with a divided, adjustable objective lens) of Königsberg Observatory were greatly expanded by his student, Schlüter.

Schmidt (1878)

Although he does not appear to have added any new measurements of his own, Schmidt provides a useful list summarizing existing values for craters used as "fundamental points," and specifically comparing the results of Lohrmann and Mädler. In addition to the astronomers mentioned above, he notes one crater studied by Wichmann and thirty-three by Neison

Hartwig (1877-1922)

Inspired by Bessl’s work, E. Hartwig produced three series of similar measurements: Strassburg (1877-1879), Dorpat (1884-1885) and Bamberg (1890-1922). The Strassburg measurements were reduced by Hartwig, the Bamberg ones (in part) by Naumann in 1939 and the Dorpat series by Koziel in 1948-9.

Franz (ca. 1890)

J. Franz initially reduced Schlüter’s Königsberg heliometer data to obtain the selenocentric longitude and latitude of Mösting A, as well as its distance from the Moon’s center and the inclination of the lunar equator to the ecliptic. He then established a system of nine additional heliometer-determined fundamental control points: Aristarchus, Byrgius A, Fabricius K, Gassendi Zeta, Macrobius A, Nicolai A, Proclus and Sharp A. Franz was also a pioneer in the use of photographic plates to determine accurate lunar positions. Beginning in 1899, he measured 150 small bright points (mostly craters) on five plates taken with the 36 inch refractor at the Lick Observatory in 1890-91. He was also able to determine the absolute heights of 55 craters, producing the first contour map of the Moon, although it was in error. He eventually estimated the positions of 1300 points, but with less accuracy than the original 150. His best points are said to be accurate to a about one arc minute (0.02 degrees) on the Moon.

Saunder (1900-1910)

This was another early attempt at developing a network based on careful measurements of positions on lunar photographs. Saunder measured 1433 lunar surface features on four plates that had been taken at the Paris Observatory in 1895-99. The overall calibration was adjusted to match measurements of about 30 fundamental points measured at the eyepiece by himself and/or Franz. Saunder later re-measured the Paris points on two plates obtained by G. W. Ritchey using the 40 inch refractor at the Yerkes Observatory in 1901, and added others bringing the total in his network to 2885. Unfortunately Ritchey failed to record the date on which his plates were taken, so there is some doubt about the reliability of the measurements. Saunder, who concentrated on the Moon’s central regions, combined his measurements with those of Franz, who had concentrated on the limb, producing a combined catalog with 3,500 distinct points. For many years this was the best available cartographic network, and it served as the primary basis for the positions of named features listed the IAU’s Named Lunar Formations of 1935.

Hayn (1904-1914)

Friedrich Hayn made micrometer measurements of the positions of five craters using the 12-refractor at Leipzig, and re-evaluated Franz’ libration constants.

The Kazan Series (1895-1945)

These consist of additional heliometer measurements made at the Engelhardt Observatory in Kazan. The data were collected by Krasnov (1895-98), Mikhailovski (1898-1905), Banachiewicz (1910-1915), Jakovkin (1916-1931), Belkovich (1932-1942) and Nefedyev (1938-1945).

Koziel (1963)

Koziel used a modern electronic computer to combine 3,282 heliometer measures to obtain improved values for the libration constants and the average longitude and latitude of Mösting A.

Schrütka-Rechtenstamm (1958)

Schrütka, together with Josef Hopmann, re-analyzed Franz’s data using a better model of the Moon’s librations than was available to Franz. His revised positions for these points severed as the basis for numerous later control networks, for example, the early LAC maps.

Arthur, Whitaker and Moore (1958-9)

These workers initiated a program of star-trailed lunar photography using the 40-inch Yerkes refractor. This is said to have permitted positions to be determined without reference to a theory of the Moon’s rotation.

Baldwin (1963)

R. B. Baldwin measured 696 features on five photographs taken, like Franz’, with the 36 inch refractor of the Lick Observatory, but at different phases. His measurements were tied to Franz’ 150 points as reduced by Schrütka, and libration constants supplied by C. B. Watts of the U.S. Naval Observatory. His estimates of their three-dimensional relationships led to a first reasonably reliable estimate of the figure (shape) of the Moon.

AMS Lunar Control System (1964-5)

The Army Map Service produced two catalogues: the AMS 1964 (with 256 features) and Group NASA 1965 (with 496 features concentrated in belts 10 degrees from the Moon’s center). The measurements were based on a total of 19 short exposure plates taken with the 36 inch refractor at Lick Observatory between 1936 and 1945 at a variety of phases. Measurements were adjusted by a least squares procedure to achieve an overall consistency with the IAU coordinates of 1935. AMS 1964 included two craters whose derived heights were more than 10 km above the others.

ACIC Selenodetic System (1965)

A network of approximately 196 primary and about 700 supplementary control points used for many of the LAC and AIC charts. The primary control net was measured on near fu1l moon photography, including eight differently librated plate sequences taken at the Pic du Midi Observatory and one at the Naval Observatory at Flagstaff, Arizona. The Pic du Midi sequences consisted of a series of five short exposures, while that from the Naval Observatory photography consisted of three long exposures taken about one minute apart. All 196 primary points were measured an each plate in every sequence. The supplementary points consisted of craters from three to twenty kilometers in diameter (most less than ten kilometers in diameter), measured on photos taken at other phases.

DOD Selenodetic Control System (1966)

A combination and re-calculation of the The AMS Lunar Control System, with certain questionable points removed, was re-calculated yielding 484 features which were combined with the ACIC Selenodetic System giving a total of 734 control points. In the view of the anonymous author of the review in S this was “not ... an optimum combination of the ACIC and AMS control works.”

Kiev Lunar Triangulation (1967)

Gavrilov’s "Catalogue of Selenocentric Positions of 500 Basic Points on the Moon's Surface" was based on photographs obtained at the Main and Pulkovo Observatories. 160 base points were measured on 16 near full moon plates, including 150 features from the Schrütka system and 70 points measured in the Baldw.in system. A composite catalogue was then developed from the three sources. The Kiev Triangulation differs from the others in that Gavrilov attempted to transform the measurements into positions relative to the Moon’s center of mass rather than its center of figure (as had been done in the past)

Manchester Selenodetic Control System (1967)

906 features were measured on 18 differently librated sequences taken near full moon with the 24 inch Equatorial Coude refractor at Pic du Midi Observatory in 1960-1961. Each sequence consisted on six short exposures. Features selected for measurement were 5-6 kilometers in size and included splash craters, mountain peaks, and other albedo points, visible at full moon. Overall calibration was tied to the system of Schrütka.

Tucson Selenodetic Triangulation (1968)

This is reportedly the first effort more-or-less independent of Franz. The positions of 48 features as measured on 25 star-trailed plates from the Yerkes Observatory. The positions of 1355 features were then related to these on 37 differently librated observations, including three Yerkes plates, six from Saunder, six from Gavrilov, and 22 from ACIC.

Manchester Selenodetic Control System (1971)

This consists of the publication of revised positions for 700 points in the Manchester Selenodetic Control System (1967).

Positional Reference System (1969)

This is a temporary system developed by the predecessors of the DMA for production of its hemispheric views of the Moon. The ACIC Selenodetic System (1965) was extended to the Moon’s farside using Lunar Orbiter photography, and was thought to be accurate to 3-13 km.

Apollo Zone Triangulation (1969)

This consists of approximately 3200 points in a zone bounded by longitude +/-20 degrees and with longitudes between 75°W and 55°E. The points were measured on Lunar Orbiter IV photographs. According to the anonymous author of the review in Schimerman, because of difficulties with the interpretation of the Lunar Orbiter photographs, “this developmental triangulation work did not attain its objective of providing a precise unified control system covering the principal portion of the Apollo Zone.”

Landmark Tracking Control System

Positions of 19 very small lunar landmarks (including 6 farside points) were determined based on visual measurements made by orbiting astronauts using a sextant and computed based on the position of the spacecraft at the time of the observation. Landmark tracking observations were performed on Apollo Missions 8, 10, 11, 12, 14 and 15. The positions of the 19 points are thought to known to a one-standard-deviation accuracy of about 900 meters horizontally and 400 meters vertically. Next to the Lunar Ranging Retroreflectors and the Apollo ALSEP transmitter locations, they are thought to be the most accurately known absolute positions on the Moon.

Local Control Systems

A great number of local control systems were developed by the DMA to support its mapping efforts for potential Apollo landing sites. These typically consist of measurements of the positions of features relative to one another on Lunar Orbiter, or possibly Apollo Metric Photos. However, the overall calibration is often based on nothing more than an informed guess as to the true coordinates of the initial point. A list of these can be found in the Section 3 of Schimerman.

Apollo Mission Control Systems

The lack of an accurately recorded time of exposure made hand-held photography from Apollo 8, 10, 11, 12 and 14 unusable for determining accurate positions. This problem was corrected on Apollo 15, 16, and 17. Despite the limitations, control networks for limited regions were derived from Apollo 10 and 12, by determining the relation of points recorded in the photos to the Landmark Tracking Points. Much more extensive networks were established for the areas of the Moon covered by the Apollo 15 Metric camera, initially in April, 1973, but later extended with Apollo 16 and 17 data, and re-evaluated in November, 1973. There is a separate Apollo 17 system, completed in April 1974. The system was further refined by constraining the vertical measurements to results from the Apollo Laser Altimeter experiments. These Apollo networks form the basis of the positions reported on NASA’s LM, LTO and Topophotomap series. The ultimate Apollo network was the Selenocentric Geodetic Reference System completed in 1976 by a team composed of National Oceanic and Atmospheric Administration and U.S. Geological Survey personnel. It again covers only the regions of the Apollo 15-17 metric photography, and is said to exhibit systematic differences of up to 2 km with respect to the other Apollo control networks. Subsequent to the Apollo missions, precise earth-based measurements were made on the Lunar ranging retroreflectors left at the Lunakod II and Apollo 11, 14 and 15 sites; and on radio transmissions from the Apollo 12, 14, 15, 16 and 17 sites, resulting in the release of positions for those points issued in 1973-1975.

Positional Reference System (1974)

This is a refinement of the 1969 Positional Reference System for the whole Moon, adjusted to accommodate the Apollo 15 Control Network, and preliminary triangulation of Apollo 16 photography. The results were thought to be accurate to 1-16 km.

January 1975. “Report on the Lunar Positional Reference System (1974)”. DMAAC.

Catalog of Lunar Positions (1975)

This DMA-produced catalog is perhaps the same as the Positional Reference System (1974)

Meyer (1980)

Meyer determined an earth-based telescopic control network using 1156 points measured on 10 plates taken over an 11 year period at the U.S. Naval Observatory, Flagstaff. 130 of the points lie in the region covered by he Apollo metric photography.

1987 ULCN

This first draft of the Unified Lunar Control Network, confined to the Moon’s nearside, consisted of 130 craters from the Apollo metric control networks, 1026 from Meyer’s 1980 earth-based telescopic network, and 10 craters from Mariner 10, all compared to results from laser and radio ranging. Of the three main networks produced by the Apollo map makers (referred to as DMA/A-15, DMA/603 and NOS/USGS), the one called DMA/603 was found to be most consistent with the laser/radio results and was used to adjust the scaling and rotation of the other networks.

1994 ULCN

The 1994 ULCN (previously announced as the 1993 ULCN) is a re-computation and extension to the farside of the 1987 ULCN. The 1478 points are compiled from the following sets:

911 points out of 1156 measured on 10 plates taken over an 11 year period at the U.S. Naval Observatory, Flagstaff, as published by Meyer (1980), but adjusted to fit the Apollo metric maps.

304 points from the Apollo Control Network, including 130 telescopic features from the Defense Mapping Agency's 1975 Catalog of Lunar Positions with coordinates re-evaluated by offsets from the "pug points" defining.

200 points out of 212 measured on images obtained during the December 7, 1992 lunar flyby of the Galileo spacecraft

63 points out of 156 measured from the lunar flyby of Mariner 10 on November 3, 1973.

The three-dimensional positions are expressed in the mean Earth/polar axis system, which, according to Davies et al. is the one normally used for lunar cartography, but a little different from the Apollo Control Network used for NASA's LTO series of lunar charts. Unfortunately, the 1994 ULCN does not cover the entire lunar surface. Coverage is especially sparse, or non-existent, on the Moon's farside. 1286 of the 1994 ULCN points are on the nearside (longitude<90 degrees); but only 192 are on the farside (longitude>90 degrees).

The Clementine Control Network (1997)

The Clementine Control Network was, like the 1987 and 1994 ULCN, primarily the work of Merton Davies and Tim Colvin, and consisted of 271,634 points on 43,871 Clementine images. It was used to determine the basic geometry of the Clementine 750-nm Basemap Mosaic, such as it appears, for example in the USGS’s PDS Map-a-Planet service. It appears that the results were never published, but it seems that the methodology used was seriously flawed, so features displayed using this system may be displayed up to 15 km or more from their true selenodetic positions.

ULCN 2005

The Unified Lunar Control Network 2005 has expanded the 1994 ULCN to 272,931 control points covering the entire Moon by adding points from the failed Clementine Control Network re-evaluated in a poorly explained fashion. The points in ULCN 2005 consist not of lunar surface features, but rather of pixel locations on specific Clementine frames. Use of ULCN 2005 therefore requires retrieving those exact frames and attempting to correlate an observed feature with its expected position in them. However, since the expected position of a feature varies depending on its height and the angle of view, the exact procedure that needs to be used appears to be undefined. Individual Clementine images cover extremely small areas, and exactly how the overall registration of the farside was achieved is not explained.

LRO/LOLA

In June 2012 the IAU Planetary Gazetteer updated the coordinates used for named lunar features to the reference system used by the Lunar Orbiter Laser Altimeter (LOLA) experiment on the Lunar Reconnaissance Orbiter (LRO) spacecraft. The ULCN 2005 positions were retained as a alternative set of historical interest.

Additional Information

The most precisely known positions on the Moon are the locations of the optical retroreflector arrays placed on the surface at the Apollo 11, 14, and 15 and Lunokhod 2 sites (tracked by laser ranging from observatories on Earth); and the five ALSEP (Apollo lunar surface experiment package) transmitters left by Apollo 12-17 (located by radio interferometry). Earth-based astronomers can determine the three dimensional locations of these objects in space to high accuracy. The absolute locations of the ALSEP transmitters are thought to be known withing about 30 meters, and the Laser Reflectors to less than 1 meter. However, translating these into positions in the selenodetic coordinate system (similar to longitude and latitude on Earth), requires assumptions about how the Moon's reference axis are oriented. A paper by Davies and Colvin (2000) gives what are thought to be the correct coordinates of these devices in the so-called "mean-Earth" system, as well as the coordinates of the Apollo landers and a number of features at the Apollo landing sites. Ideally lunar control networks are tied to these well-determined points.

The most recent lunar control networks of note are the 1994 ULCN and ULCN 2005. The 1994 ULCN is a compilation of several earlier networks, most of the points being Earth-based. ULCN 2005 is an effort to correct the flawed Clementine Control Network and reconcile it with the 1994 ULCN.

In my personal opinion, the 1994 ULCN continues to be the most useful for calibrating photographs. Each point it contains corresponds to a recognizable feature on the lunar surface (most probably representing the center point of a crater rim). ULCN 2005 adds many points, but the new points do not correspond to physical places on the Moon's surface. Many of the 1994 ULCN points have been adjusted slightly in position, but it is not yet clear if averaging their positions with thousands of ill-defined new points improves their accuracy or not. - JimMosher

As of 2012, coordinates of named lunar features in maps of the Lunar Section - found in the IAU’s Working Group for Planetary System Nomenclature (WGPSN) website - are now available in the LOLA (Lunar Orbiter Laser Altimeter) reference frame. Map coordinates for lunar features were previously referenced from data using the Unified Lunar Control Network (ULCN 2005) framework that are still viewable through the above IAU Gazetteer site, however, these data sets have now been relegated to archival status, and will no longer be updated. - JohnMoore2Jun 2, 2011

Fundamental Points on the Moon

The following table from Davies and Colvin (2000) lists the nine best-determined locations on the Moon in what is called the Mean-Earth/Polar Axis coordinate system:

Based on these positions and the known offsets of these devices from the Apollo lunar landers, Davies and Colvin (2000) also estimated the locations of the six Apollo Lunar Modules:

Table 2: Estimated Locations of Lunar Modules

Mission

Latitude, °N

Longitude, °E

Apollo 11

0.67408

23.47297

Apollo 12

-3.01239

-23.42157

Apollo 14

-3.64530

-17.47136

Apollo 15

26.13222

3.63386

Apollo 16

-8.97301

15.50019

Apollo 17

20.19080

30.77168

They also gives precise coordinates and diameters for an additional 47 features, ranging in size from 14 to 2150 m, at the 6 Apollo landing sites. Like the Lunar Module locations, they were determined by offsets from the known LRRR and/or ALSEP locations as depicted on NASA maps of the sites.

It should be noted that the history of selenodesy is replete with examples of scientists overestimating the accuracy of their position values by a factor of 10 or more. So claims that the absolute locations of the laser retroreflectors or ALSEP radio transmitters are known to “xx” accuracy should be viewed with extreme skepticism.

In the cases of Apollo 15, 16 and 17, the Davies-Colvin deduced Lunar Module positions can be compared to the positions plotted on NASA-prepared Topophotomaps. The positions obtained by plotting the Davies-Colvin coordinates using the scales provided on those maps differ from the NASA-plotted positions by about 350 meters. This probably reflects a difference in the control systems used, with the Davies-Colvin one probably being more accurate. However, when plotted on the Topophoto and/or Site Transverse maps, the pattern of the 47 landing site features listed in the paper, supposedly read from those maps and treated as offsets from the astronomically determined ALSEP or LRRR anchor points, does not precisely match the pattern of features shown there. It would appear some errors must have been made in scaling positions from the maps or in applying the offsets, and it is very hard to believe all the positions listed in Davies-Colvin could be accurate to the many decimal points to which they are stated. None of this should be taken to indicate that there is any uncertainty as to where the Apollo Lunar Modules are located relative to observable features -- only that there is some uncertainty as to the precise coordinates that should be assigned to those features.

A highly technical article by Chapront et al. also gives precise selenodetic positions for the four laser retroreflectors. When expressed in the Mean Earth-Polar Axis system they appear to be quite close to those of Davies and Colvin; but in the Principal Axis system they are quite different.

LPOD Articles

Bibliography

Lunar Control Networks -- lists data and gives references for the 1994 ULCN; also describes the flawed Clementine Network